Field of the Invention
This invention relates to an active-matrix type liquid crystal display device and, more particularly, an active-matrix type liquid crystal display device with an array substrate including three-terminal non-linear switching elements connected to pixel electrodes.
An active-matrix type liquid crystal display device (called hereinafter the "AM LCD") includes array and counter substrates with alignment layers on opposite surfaces, respectively, and a liquid crystal composition held between the substrates. A plurality of signal and scanning lines are disposed on the array substrate in a matrix form. Thin film transistors (herein after called "TFTs") are formed in the vicinities of cross points of the signal and scanning lines as three-terminal non-linear switching elements, respectively. Pixel electrodes made of indium tin oxide (hereinafter called the "ITO") are also provided in those vicinities.
Light blocking layers are provided on a glass substrate of the counter substrate in a matrix form to prevent incident light from coming from the vicinities of pixel electrodes. Counter electrodes made of ITO are disposed on the light blocking layers through insulation layers.
The signal and scanning lines are electrically connected to a driver circuit board through polyimide flexible printed circuit boards on which metal wiring is formed or flexible printed circuit boards on which active elements are provided by tape automated bonding or the like.
The counter electrode is conducted to the array substrate through transfers made of resins into which conductive particles such as silver ones are dispersed. The counter electrode is further electrically connected to the driver circuit board through the flexible printed circuit boards.
Generally, crosstalk images are seldom caused in the AM LCD set forth above but occur once in a while.
When a black or white window pattern, for instance, is displayed on a halftone raster background in such a driving method that the polarity of a voltage applied to pixel electrodes is reversed every signal line with respect to a reference potential, crosstalk components appear at the upper and lower portions of the window pattern. This phenomenon results from leakage currents flowing through the TFTs and the potential of a pixel electrode approaching that of a signal line. The capacitance value of a storage capacitor is designed to be larger to avoid the crosstalk images in the longitudinal direction of the display.
In the driving method where the voltage applied to the liquid crystal is changed every scanning line in polarity with respect to a reference potential, when a black or white window pattern is displayed on a halftone raster background, crosstalk components appear on the right and left sides of the window pattern. This is caused by potential fluctuations at the counter electrode or the storage capacitor, i.e., fluctuations of the voltage applied to the liquid crystal. As one of the measures to obtain good display images without such lateral crosstalk components, resistance values of the counter electrode and storage capacitor lines are made small to perform the potential polarity inversion quickly.
Highly functional software, such as WINDOWS (a registered trademark owned by Microsoft Corp.) Version 3.1 or WINDOWS 95, has been developed for personal computers to perform more efficiently and is widely used at the present. The software makes it easily possible to display sophisticated patterns which were impossible to be made in the past.
In the driving method of AM LCDs where potentials at the counter electrode and at the storage capacitor lines are changed every scanning line and the polarities of voltages applied to the liquid crystals are inverted in response thereto, when a window pattern based on the advanced performance software is displayed on a background consisting alternatively of black and halftone pixels at each scanning line, crosstalk images appear at the upper and lower portions of the window pattern in spite of the AM LCDs with the crosstalk prevention measure mentioned above.